Studies will be conducted on the contractile protein myosin of cardiac and skeletal muscle, as follows: 1. Characterization of subunit composition of myosin, by ultracentrifugal, electrophoretic, and other methods. 2. Studies on possible structural changes in cardiac myosin, as related to cardiac hypertrophy, failure, and other disease processes. 3. Studies on myosin ATPase, including hybridization experiments on role of subunit specificity in myosin ATPase; experiments on the interaction of nucleotide, Ca ions and Mg ions, and myosin subunits; and pressure effects on steady-state kinetics of myosin ATPase.